In practice, aqueous preparations and especially suspensions, dispersions or slurries of water-insoluble solids such as minerals, fillers or pigments are used extensively in the paper, paint, rubber and plastics industries as coatings, fillers, extenders and pigments for papermaking as well as aqueous lacquers and paints. For example, suspensions or slurries of calcium carbonate, talc or kaolin are used in the paper industry in large amounts as filler and/or as a component in the preparation of coated paper. Typical aqueous preparations of water-insoluble solids are characterized in that they comprise water, a water-insoluble solid compound and optionally further additives, such as dispersing agents, in the form of a suspension, a slurry or dispersion with a water-insoluble solid content of 1 to 80 wt.-% based on the total weight of the preparation. A typical aqueous preparation is a White Mineral Dispersion (WMD) having a solids content of 45 to 78 wt.-%. Water-soluble polymers and copolymers which may be used as e.g. dispersant and/or grinding aid in such preparation are, for example, described in U.S. Pat. No. 5,278,248.
The aforementioned aqueous preparations are often subject to contamination by microorganisms such as aerobic and anaerobic bacteria resulting in changes in the preparation properties such as changes in viscosity and/or pH, discolorations or reductions in other quality parameters, which negatively affect their commercial value. Therefore, the manufacturers of such aqueous preparations usually take measures for stabilizing the suspensions, dispersions or slurries. For example, it is known that aldehyde-releasing biocides reduce the growth and accumulation of such microorganisms in aqueous preparations and, thus, reduce the tendency of undesired alterations of these preparations, like viscosity changes or unpleasant odours.
For ensuring an acceptable microbiological quality of aqueous preparations, preservatives or biocides are used over the entire life cycle of the preparation (production, storage, transport, use). In the art, several approaches for improving the microbiological quality of aqueous preparations have been proposed. For example, EP 1 139 741 describes aqueous suspensions or dispersions of minerals, fillers and/or pigments, containing a microbiocidal agent in the form of a solution and derivatives of phenol in partially neutralized form. U.S. Pat. No. 5,496,398 relates to a process for the reduction of microorganisms in kaolin clay slurries by a combination of low temperature heat and reduced levels of a microbiocidal agent. WO 02/052941 describes biocide compositions for incorporation into paints, coating, plasters and plastics comprising at least one metal oxide and at least one metal salt. US 2006/0111410 mentions a mixture comprising 1,2-benzisothiazolinone (BIT) and tetramethylolacetylenediurea (TMAD) for protecting industrial materials and products against attack and destruction by microorganisms. Furthermore, it is suggested in the art to add formaldehyde-releasing substances to such aqueous preparations for improving the microbiological quality. For example, U.S. Pat. No. 4,655,815 mentions a antimicrobial composition comprising a formaldehyde donor. Furthermore, WO 2006/079911 describes a method of protection against microorganisms by increasing the OH− ion concentration of the suspension.
WO 2004/040979 A1 relates to synergic antimicrobial mixtures containing 1,2-benzisothiazolinon (BIT) and benzylhemiformal (BHF). The corresponding mixtures are used, for example, for slurries of pigments. WO 2004/040979 A1 is not concerned with the treatment of aqueous preparations containing strains of bacteria which are resistant to, tolerant to and/or degrade aldehyde-releasing biocides. EP 1 661 587 A1 relates to germicidal compositions including phthalaldehyde as an active ingredient. It is indicated in EP 1 661 587 A1 that carbonate salts and bicarbonate salts may enhance the germicidal efficacy of phthalaldehydes. However, EP 1 661 587 A1 is not concerned with the treatment of aqueous preparations containing strains of bacteria which are resistant to, tolerant to and/or degrade aldehyde-releasing biocides.
US 2001/0009682 A1 relates to disinfectant concentrates having improved biocidal activity which may contain an aldehyde such as glutaraldehyde, a glycol and a lithium based buffer. It is described in US 2001/0009682 A1 that the buffer is required to control the pH of both the concentrate and its dilutions within the desired biocidal effective range. Also US 2001/0009682 A1 is not concerned with the treatment of aqueous preparations containing strains of bacteria which are resistant to, tolerant to and/or degrade aldehyde-releasing biocides.
Because of the limited activity spectrum of several biocides, the efficacy of such biocides against bacteria is not always satisfactory if strains of bacteria are present which are resistant to, tolerant to and/or degrade such biocides, and, thus, the obtained action is in some cases insufficient to avoid microbially induced alteration of aqueous preparations.
Thus, there is still a need for adequate compositions providing sufficient biocidal activity in aqueous preparations such as suspensions, dispersions and slurries of water-insoluble solids in order to achieve a longer lasting and sufficient stabilization.